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Moon and Regulus

StarDate:

February 24, 2013

When you look into the night sky, all of those little pinpoints of light look pretty much the same. A few are brighter than the others, and a few show some color, but otherwise, there’s little difference.

From up close, though, it’s a different story. Consider Regulus, the bright heart of Leo, the lion, which is close to the left of the Moon this evening.

To the eye alone, Regulus is simply an unusually bright star. But telescopes reveal that Regulus is actually two stars — the big, bright one that we can see, plus a tiny stellar corpse known as a white dwarf. And the bright star is quite different from our own Sun — it’s about a third bigger through the equator than through the poles.

That squashed appearance is caused by the star’s high-speed rotation — it makes one full turn every 16 hours, compared to almost a month for the smaller Sun. That rapid motion may be the result of interactions with its tiny companion.

The companion probably began life as the bigger and heavier of the two stars. Because of its greater mass, it aged more rapidly, quickly puffing up to giant proportions. As it grew, it began dumping gas on its companion — the bright star we see as Regulus. That increased Regulus’s mass and caused it to spin faster. Regulus eventually took most of the other star’s gas, leaving an unusually small white dwarf — and a star system that’s quite different from most of the others that sprinkle the night sky.

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